80 J C.S. Perkin IStrain Factors in Quinquecovalent Phosphoranes. Sulphur-containingRings and Six-membered RingsBy Stephen A. Bone, Stuart Trippett," and Peter J. Whittle, Department of Chemistry, The University,ieicester LE1 7RHVariable-temperature n.m.r. spectroscopy on a range of spirophosphoranes has given data on the increase in energywhen five-membered rings containing sulphur attached to phosphorus move from a diequatorial to an apical-equatorial position in a trigonal-bipyramidal phosphorane. The results have been compared with those from thecorresponding oxygen-containing systems and the remarkable similarity has been explained in terms of compen-sating lone-pair orientation and strain terms. Lone-pair orientation effects are also important in determining thepreference of six-membered rings containing heteroatoms attached to phosphorus for an apical-equatorial asoppose to a diequatorial disposition in trigonal bipyramidal phosphoranes.PREVIOUSLY we analysed the preference of five-mem-bered rings for an apical-equatorial (1) as opposed to adiequatorial disposition (2) in trigonal bipyramidalZA:! -AA H(1) ( 2 )phosphoranes in terms of three factors: (a) an increase inangle strain on increasing the ring angle at phosphorusfrom 90 to 120deg;, (b) a change in apicophilicity in thegroups occupying the apical positions, and ( c ) the pre-ference of lone-pairs on equatorial heteroatoms for theequatorial plane. In these terms the difference in energybetween (1) and (2) can be expressed as equation (i),AE = S + R X + RY + AA(Y - 2)where R X and RY are the energies of rotation aroundequatorial XP and YP bonds, respectively, and AA(Y -2) is the difference in apicophilicity between the groupsY and 2 determined in acyclic systems when lone-pairsare free to adopt their preferred orientations. ThisS.A. Bone, S. Trippett, and P. J. Whittle, TetyahedronLetters, 1974, 1795.2 S. C. Peake and R. Schmutzler, Chem. Comm., 1968, 1662;J . Chem. SOC. ( A ) , 1970, 1049.E. L. Muetterties, P. Meakin, and R. Hoffmann, J . Amer.Chem. SOC., 1972, 94, 3047.(i)analysis gives good agreement with experiment a1 datafor oxygen- and/or nitrogen-containing five-memberedrings when S (saturated) = 8 kcal mol-l, S (unsaturated)= 10 kcal mol-l, R N = 10 kcal mol-l, and R O is estimatedat 5 kcal mol-l.This paper is concerned with the similarpreferences of five-membered sulphur-containing ringsand of six-membered rings in general.Fiae-membered Rivtgs codaifling Sulphur attached toPhosphor.us.-The barrier to rotation around equatorialPS bonds is known2 to be comparable to that aroundequatorial PN bonds and considerably greater than inthe case of PO bonds? Furthermore, the groups RO andRS are known to have similar apicophilicitie~.~ Itfollows from equation (i) that if X or Y is changed fromoxygen to sulphur, and if we assume that the strain termis unchanged, then the energy difference between (1) and(2) would be expected to increase by the difference in therotational energies round equatorial PO and PS bonds,i.e.by ca. 6 5 kcal mol-l.The pseudorotational pathways open to a spirophos-phorane can be illustrated by reference to the hexa-fluoroacetone adduct (3; A-D all CF,). The moststable conformers of this molecule are probably thetopomers (3) and (euro;4): although (5) and (6), with apicalD. U. Robert, D. J. Costa, and J. G. Riess, J.C.S. Ckem.S . A. Bone, S . Trippett, and P. J. Whittle, J.C.S. Pevkin I ,E. Duff, D. R. Russell, and S. Trippett, Phosfihorus, 1974, 4,Comm., 1973, 745.1974,2125.2031977 81sulphur, will be of only slightly higher energy and thepseudorotations (3) @ (6) and (5) T- (8) will be1( 5i'AJtrapid on the n.m.r. time-scale at accessible temperatures.These pseudorotations do not make any of the CF, groupsequivalent, and at room temperature the 19F n.m.r.spectrum would be expected to show four equal signals.At higher temperatures the pseudorotations via the high-energy phosphoranes (4) and (7), having diequatorialoxathiaphospholan rings, will become rapid on the n.m .rtirrie-scale, leading to equivalence of the CF, groups Aand D, and B and C, and to simplification of the n.m.r.spectrum to two signals.Pseudorotations via high-energy phosphoranes such as (9) with a diequatorialtetrakistrifluoromethyldioxaphospholan ring are knownto be slow on the n.m.r. time-scale at 180 "C; if rapidthey would lead to equivalence of the CF, groups A andB, and C and D. As before: the assumption is madethat high-energy phosphoranes with diequatorial ringscan be regarded as equivalent to transition states be-tween low-energy phosphoranes. The free energy ofactivation for the process leading to simplification of thel9F 1i.m.r.spectrum is therefore a measure of the energydifference between (4) and (3).Table 1 gives the free energies of activation for placingvarious five-membered sulphur-containing rings diequa-torial with phenoxy moving to an apical position andcompares these with the values in the correspondingsystems where sulphur has been replaced by oxygen.The change from sulphur to oxygen does not affect theA. S. Pell and G. Pilcher, Trans. Faraday Soc., 1965, 61, 71.S. A. Bone and S. Trippett, Tetrahedron Letters, 1975, 1583;S. Antczak, S. A. Bone, J.Brierley, and S. Trippett, J.C.S.Perkin I , in the press.J. I. Dickstein and S. Trippett, Tetrahedron Letters, 1973,2203.lo N. J . De'Ath and D. B. Denney, J . C . S . Chem. Comm., 1972,396.energy of activation significantly, a surprising result inview of the prediction made earlier. However, thatprediction was based on the assumption that the strainfactor would remain constant, which is probably not thecase; sulphur is much more able than oxygen to accom-modate angle strain. Pell and Pilcher have shown,from heats of combustion, that tetrahydrofuran has3.7 kcal mol-l more strain than tetrahydrothiophen, adifference which increases to 5.9 kcal mol-l in the corres-ponding 'etans and to 7.5 kcal mol-l in the 'irans. Theincrease in R X and/or RY in equation (i) on changing Xand/or Y from oxygen to sulphur, due to the greaterenergy of rotation round equatorial PS than round PObonds, is therefore being offset by a decrease in the strainterm, S, due to the greater ability of sulphur to accom-modate the increase in angle strain.Preparation of the spirophosphoranes (3) and (10) bythe N-chlorodi-isopropylamine method has recently beendescribed.* 4,4,5,5-Tetramethyl-l-phenoxy-l,3 ,Z-di-oxaphospholan with perfluorobiacetyl gave (1 1 ; X =0), with 3,4-bistrifluoromethyl-1,2-dithieten lo gave (11;X = S), with monothiobenzil l1 gave (12; X = S) , andwith benzil gave (12; X = 0).As expected, in view of the poorer apicophilicity of thedimethylamino-group relative to the phenoxy-group,13the lH n.m.r.spectra of the phosphoranes (13) and (14)did not change in the range from room temperature to175 "C.(13) .* (14)'8Six-membered Rz.rzgs.-Calculations l3 have indicateda preference of the phosphorinan ring for a diequatorialposition in a trigonal bipyramidal phosphorane but onlylimited experimental data are available on this preference.The fluorine atoms in the trifluorophosphorane (15) arestill not equivalent in the laF n.m.r. spectrum at 100 OC,14showing that AG* for the pseudorotation (15) (16)is 16 kcal mol-l, whereas the barrier to the pseudorot-ation (17) + (18) in the corresponding five-memberedtrifluorophosphorane is 7-8 kcal mol-l. The relief ofstrain in the five-membered ring on going from (17) to(18) is 8-9 kcal mol-l; it follows that any change instrain in the six-membered ring on going from (15) to (16)is small and may be riegative.The introduction into the six-membered ring of hetero-atoms attached to phosphorus means that lone-pair11 B.A. Arbuzov, N. A. Polezhaeva, V. V. Smirnov, and A. A.Musina, Izvest. Akad. Nauk S.S.S.R., Ser. klaim., 1975, 1658.12 S. Trippett and P. J. Whittle, J . C . S . Perkin I , 1973, 2302.13 P. Gillespie, P. Hoffmann, H. Klusacek, D. Marquarding, S.Pfohl, F. Ramirez, E. A. Tsolis, and I. Ugi, Angew. Chem.Internat. Edn., 1971, 10, 687.l4 E. L. Muetterties, W. Mahler, and R. Schmutzler, Inorg.Chem., 1963, 2, 613; R. Schmutzler, Angew. Chem. Internat. Edn.,1975, 4, 49682 J.C.S. Perkin Iorientation effects have to be taken into account.Ex- phorus compounds. Data on their variable-temperatureamination of Drieding models, containing sp2-hybridised 19F n.m.r. spectra are given in Table 2. The increasingheteroatoms, shows that in both an apical-equatorial complexity of the spectra at low temperatures (1chair ring and in the only conformer of a diequatorial peak .--) 2 peaks) when X = Y; otherwise 2 --+ 4 isTABLE 1N.m.r. data a on spirophosphoranes(10) 'cF3Phx-P,(12) *-AJ..OPh"C F3OPh'CF3OPh94 94 17.7O 17.4'143 54 20.7" 20.5l136b 4.5 22.3 134V 2 22.9104 3.5 20.7.f 120 4.5 21.4a In l-bromonaphthalene unless otherwise stated. Two signals coalesce to one. amp;2 "C. d f 0 . 3 kcal mol-1; calculated by usingthe Gutowsky Holm equation.leF a t 94.1 MHz. f lH at 100 MHz. In CBrC1,.ring the lone-pairs on equatorial atoms are in unfavour-able orientations. Only with an apical-equatorial boatFF -P '2W I Fring is it possible for the lone-pair on the equatorial atomto be in the favoured equatorial plane.From the low-temperature lH n.m.r. spectra of severalphosphoranes containing 113,2-dioxaphosphorinan ringsDenney l5 concluded that this ring has a preference for anapical-equatorial position.The adducts (19) were prepared by the addition ofhexafluoroacetone to the appropriate tervalent phos-associated with slowing of the pseudorotations (19)(20) which place the six-membered rings diequatorial.The barrier to this process clearly depends on the natureof the atom which remains equatorial showing that lone-pair orientation effects are playing a significant part,although changes in the rotational energy round theTABLE 2lSF N.m.r.d a t a a on t h e spirophosphoranes (19)X Y Tc AvIHz AG*0 0 - 140 100 5.9MeN 0 -- 70 102 9.2MeN MeN - 140 6a In ether-light petroleum. 5 3 "C. 5 0.3 kcal niol-l.equatorial bond are not fully reflected in the height ofthe barrier.The barrier to rotation round equatorial PO bonds isknown to be (8 kcal mol-l and we have estimated avalue of 5 kcal mol-l on the basis of strain data in five-membered phosphoranes. The barrier to equivalencel5 B. C. Chang, W. E. Conrad, D. B. Denney, D. 2. Denney,R. Edelman, R. L. Powell, and D. W. White, J . Amer. Chem.SOL,1971, 93, 40041977 83of the CF, groups in (19; X = Y = 0) of 5.9 kcal mot1might therefore be associated, not with the pseudorotation(19) ---+ (20), but with slowing of rotation round theP-OPh bond. In order to assess this possibility thespirophosphorane (21) was prepared from hexafluorobi-acetyl and 2-phenoxy-l,3,2-dioxaphosphorinan and itslow-temperature 19F n.m.r. spectrum examined. The/ ' y .OPh OPh( 19)'cF3 (20) -cF3(21 )cF3spectrum remained a sharp singlet down to -145 "C,showing that even at this temperature rotation round the, equatorial P-OPh bond is rapid on the n.m.r. time-scaleand supporting the association of the non-equivalence ofthe CF, groups of (19; X = Y = 0) at low temperatureswith slowing of the pseudorotation (19) + (20).Subsequent to the work described above we havedetermined the structure of the spirophosphorane (22)by X-ray analysis.16 The apical-equatorial perhydro-oxazaphosphorine ring is a boat conformer with thelone-pair of the planar nitrogen in the equatorial plane,emphasising the importance of lone-pair orientationeffects in determining the stable conformers of phos-phoranes. If the most stable conformer of an apical-equatorial lJ3,2-dioxaphosphorinan ring is also the boatform, then (a) the energy barrier of 5.9 kcal mol-l forpseudorotation of (19; X = Y = 0) is that for moving aboat 1,3,2-dioxaphosphorinan ring from an apical-equatorial to a higher energy diequatorial position, and(b) since an apical-equatorial chair 1,3,2-dioxaphosphor-inan ring would be of higher energy than a similarlypositioned boat-form, it is not possible to prehct thepreferred location of a chair 1,3,2-dioxaphosphorinanring in a t rigonal bipyramidal phosphorane.Clearlythese considerations are relevant to the mechanism ofnucleophilic substitution at phosphoryl centres in 1,3,2-dioxaphosphorinans, and they will be discussed in detailelsewhere.EXPERIMENTALl9F N.m.r. spectra were determined a t 56.4 MHz andchemical shifts are quoted relative to internal PhCF, unlessotherwise stated. 31P N.m.r. spectra were obtained a t 24.3MHz and chemical shifts are quoted relative to external85 H,PO,. Positive shifts are upfield from the referencein both cases. lH N.m.r. spectra were obtained a t 60 MHzfor solutions in CDC1, unless otherwise stated.5-Phenoxy- 7,8-bistrifEuoromethyl-2 , 2,3,3-tetramethyl- 1 , 4-di-oxa-6,9-dithia-5-phosphaspiro4.4non-7-ene (1 1 ; X = S) .-3,4-Bistrifluoromethyl- 1,2-dithieten (1.15 g) in dichloro-methane (15 ml) was added slowly to a stirred solution of4,4,5,5-tetramethyl-2-phenoxy- 1,3,2-dioxaphospholan ( 1.2g) in dichloromethane (20 ml) at - 78 "C, and the solutionwas allowed to warm to room temperature.Evaporationand crystallisation of the residue from light petroleum gavethe title Phosphorane (95y0), m.p. 88-89.5", m/e 467, 373,240, 226, 182, 162, and 147, 7 (100 MHz; 1-bromonaphthal-ene) 9.12 (6 H, s) and 9.18 (6 H, s), lQF (CDC1,) -8.65 (d,J 0.5 Hz), (CH,Cl,) -13.6 p.p.m. (Found: C, 41.3;H, 3.8; S, 13.8.Ci,H17F,0,PS2 requires C, 41.2; H, 3.6;S, 13.7).In a similar way was prepared the 5-dimethylamino-analogue (14) (95y0), m.p. 127-128", T 7.27 (6Hl d, J 13Hz),8.62 (6 H, s ) , and 8.80 (6 H, s ) , l9F (CDC1,) -8.43, 3lP(CDC1,) -10.3 p.p.m. (Found: C , 34.6; H, 4.4; N, 3.4.C12H~,F,N0,PS, requires C, 34.5; H, 4.3; N, 3.4).2,2,3,3-Tetramethy2-5-phenoxy-7,8-diphenyl- lJ4,6-trioxu-9-thia-5-phosphaspiro4.4non-7-ene (12; X = S) .-A solutionof monothiobenzil, generated from sodium S-(a-phenylphen-acyl) thiosulphate (1.1 g), in dichloromethane (25 ml) wasadded slowly to a stirred solution of 4,4,5,5-tetramethyl-2-phenoxy-l,3,2-dioxaphospholan (0.75 g) in dichlorometh-ane (15 ml) at -78 "C. The blue colour of the monothio-benzil was immediately discharged.Evaporation, andcrystallisation of the residue from light petroleum gave thetitle phosphorane (32y0), m.p. 140-141", m/e 466, 366, 256,and 210, T 2.65-3.7 (15 H, m), 8.42 (3 H, s), 8.53 (3 H, s),8.60 (3 H, s), and 8.65 (3 H, s) (Found: C, 66.1; H, 5.9.C,,H,,O,PS requires C, 66.9; H, 5.8).In a similar way was prepared the 5-dimethylamino-analogue (15) (63), m.p. 156" (decomp.) (from ether),m/e 417, 317, 290, 257, 252, 210, and 207, T 2.95 (10 H, m),7.34 (6 H, d, J 11 Hz), 8.80 (9 H, s), and 8.91 (3 H, s) (in1-bromonaphthalene a t 100 MHz the methyl groups gavefour signals of equal intensity at T 8.85, 8.93, 8.97, and 9.11) ,(CDC1,) +22 p.p.m. (Found: C , 63.3; H, 6.9; N, 3.3.C,,H,,NO,PS requires C, 63.3; H, 6.7; N, 3.3).1,4,6,9-tetraoxa-5-fihos~huspiro4.4non-7-ene (1 1 ; X = 0).-Hexafluorobiacetyl (1.0 g ) was passed into a solution of4,4,5,5-tetramethyl-2-phenoxy- 1 , 3,2-dioxaphospholan ( 1.2g) in ether (30 ml) a t 0 "C and the solution set aside at roomtemperature for 1 h.Evaporation then gave the titlephosphorane (95), m.p. 58.5-60.5", m/e 434, 419, 377, 361,341, 334, and 317, T 2.67-3.35 (5 H, m) and 8.67 (12 H, s),l9F (94.1 MHz; CDCl,) 2.6 ( s ) p.p.m., 31P (ether) +37 p.p.m.(Found: c, 44.3; H, 4.1; P, 7.05. C,,H,,F,O,P requiresC, 44.25; H, 3.9; P, 7.15).A similar reaction gave 5-~henoxy-2,3-bistri$uoromethyl-1,4,6,1O-tetraoxa-5-~hos~has~iro 4.5dec-2-ene (88 ) , m.p.70-75" (sealed tube) (from hexane), T 2.50-3.23 (5 H, m),5.82 (4 H, dt, J 17 and 7 Hz), and 8.0 (2 H, q, J 7 Hz), 1QF(ether) +71 p.p.m.(relative to internal CFCl,), 31P +51p.p.m., m/e 392, 373, 334, 299, 259, and 254.2,2,3,3-Tetramethyl-5-phenoxy-7,8-dipheny1-l14,6,9-tetra-oxa-5-fihosphasfiiro4.4non-7-ene (12; X = 0) .-Benzil (0.7g) was dissolved in a solution of 4,4,5,5-tetramethyl-2-phenoxy- 1,3,2-dioxaphosyholan (0.8 g) in ether (2 ml) withl6 J..H. Barlow, S. A. Bone, D. R. Russell, and S . Trippett,unpublished work.2,2 , 3,3-Tetramethy2-5-phenoxy- 7,8-bistrifEuoromethyI84 J.C.S. Perkin Igentle warming and the solution set aside a t room tempera-ture overnight. Filtration and crystallisation from lightpetroleum gave the title Phosphorane (77), m.p. 122.5-123.5", m/e 450, 350, and 274, z 3.0 (15 H, s), and 8.6 (12H,s ) , 31P (CH,Cl,) +40.2 p.p.m.(Found: C, 69.35; H,6.1; P, 6.9. C,,H,,O,P requires C, 69.35; H, 6.0; P,6.8).Reaction of PII1 Compounds with Hexafluoroacetone.-Hexafluoroacetone (22 mmol) was condensed into a solutionof the PrlI compound (10 mmol) in ether (30 ml) a t - 78 "C.After 0.5 h a t -78 "C the solution was allowed to warm toroom temperature and set aside for 1 h. Evaporation, andcrystallisation of the residue than gave the following phos-phoranes in nearly quantitative yields : 5-$henoxy-2,2,4,4-tetrakistri$uo, omethyZ- 1,3,6-trioxa-9-thia-5-phosphaspi~o4.4-nonane (13), m.p. 110-112", m/e 532, 513,472,463,451, and439, z 2.8 (5 H, s) and 5.4-7.5 (4 H, m), lSF 4.1 (6 F, m) and17.1 (6 F, m) p.p.m., 31P -11 p.p.m.(Found: C, 31.7;H, 1.5; F, 43.8. Cl,H,Fl,04PS requires C, 31.6; H, 1.7;F, 43.9) ; 5-~henoxy-2,2,3,3-tetrakistrifluoromethyZ-l,4,6,10-tstraoxa-5-Phosphas~~ro4.5decane (20; X = Y = 0), m.p.93-97' (sealed tube), m/e 530, 511, 473, 461, 437, 397, and345, z 2.53-3.35 ( 5 H, m), 5.32-6.42 (4 H, m), and 7.52-8.42 (2 H, m), lSF (ether-light petroleum) 4.78 (s) p.p.m.,31P +68 p.p.m. (Found: C, 33.6; H, 2.0; P, 5.9. Cl,Hll-Fl,O,P requires C, 34.0; H, 2.1; P, 5.85); lO-methyZ-5-phenoxy-2,2,3,3-tetrakistri$uoromethyZ- 1,4,6-trioxa- lO-aza-5-phos~haspiro4.5decane (20; X = NMe, Y = 0), m.p.98.5-99" (from ethanol), m/e 543, 524, 474, 450, 422, 350,211, and 118, 7 2.65-3.25 ( 5 H, m), 5.75-7.87 (4 H, m),7.10 (3 H, d, J 10 Hz), and 7.93-8.55 (2 H, m), lSF (ether-light petroleum) 3.94 (6 F, m) and 5.39 (6 F, m) p.p.m., 31P+58 p.p.m. (Found: C, 35.5; H, 2.4; F, 41.8; P, 5.7.Cl,Hl,Fl,N04P requires C, 35.35;. H, 2.6; F, 42.0; P,5.7 ) ; and 6,10-dimethyZ-5-~henoxy-2,2,3,3-tetrakistrij7uoro-methyl- 1,4-dioxa-6,lO-diaza-5-~hos~haspir04.5decane (20;X = Y = NMe), m.p. 50-52", m/e 556, 537, 487, 463, 240,224, 166, and 147, ~2.56-3.14(5H,m), 6.66-7.62(4H,m),7.40 (6 H, d, J 12 Hz), and 8.04-8.32 (2 H, m), 1deg;F (lightpetroleum) 4.88 (s) p.p.m., 31P +37 p.p.m. (Found: C, 37.0;H, 3.0; F, 41.3; P, 5.7. C17H17Fl,N,03P requires C, 36.7;H, 3.1; F, 41.0; P, 5.6).We thank the S.R.C. and CIBA-Geigy (U.K.) Ltd. for6/1332 Received, 8th JuZy, 19763studentships
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